The IESG has approved the following document: - 'Coupled congestion control for RTP media' (draft-ietf-rmcat-coupled-cc-07.txt) as Experimental RFC This document is the product of the RTP Media Congestion Avoidance Techniques Working Group. The IESG contact persons are Mirja Kühlewind and Spencer Dawkins. A URL of this Internet Draft is: https://datatracker.ietf.org/doc/draft-ietf-rmcat-coupled-cc/ Technical Summary The RMCAT working group is developing congestion control schemes for use with RTP. When multiple such congestion controlled RTP flows traverse the same network bottleneck, combining their controls can improve the total on-the-wire behavior in terms of delay, loss and fairness. This document describes such a method for flows that have the same sender, in a way that is as flexible and simple as possible while minimizing the amount of changes needed to existing RTP applications. It specifies how to apply the method for the NADA congestion control algorithm, and provides suggestions on how to apply it to other congestion control algorithms. Working Group Summary The draft has been under development in the working group for some years. Much of the time was taken waiting for the candidate congestion control algorithms to stabilise, mapping the algorithms to the mechanisms given in this draft, and deciding which congestion control algorithms should be supported. The coupled congestion control algorithm itself has proved reasonably stable. The draft discusses how to apply coupled congestion control to NADA and Google Congestion Control. The mapping to NADA is in the main body of the draft, since NADA is nearing working group last call and believed stable. The mapping for Google Congestion Control is in an appendix, since Google Congestion Control is not yet finalised. There is no mapping for SCReAM at this time, but one could be added later if there was interest in doing so (nothing in SCReAM should prevent this). Overall, the working group process has been relatively smooth, although not rapid. The main issue of contention was the choice of congestion control algorithm to which the mechanism should be applied - based on the maturity of the candidate congestion control algorithms, and the relative importance the authors of the candidates placed on coupled congestion control. Document Quality The algorithm has been implemented in simulations and emulated testbeds. This is appropriate for an experimental protocol of this type, and meets the usual community evaluation standards for transport protocol research. The draft has been reviewed by some authors of each candidate congestion control algorithm, with Xiaoqing Zhu and Stefan Holmer providing detailed reviews and advice on integration with the congestion control proposals. The draft is well written, and the mechanism is clearly specified. There is no need for MIB Doctor, Media Type, or other expert review, since the proposed mechanism relies only on common RTP features and parameters that can be directly measured by the end-point using the mechanism. Personnel The document shepherd is Colin Perkins. The responsible AS is Mirja Kühlewind.
